If you've gone down the diy van route, then its possible to build your system so everything is quick release even the wiring, mount pump, switch, varistream etc on a board with wingnuts to the ply panelling, connect hose from tank to pump to di and reel with hozelocks, with a bit of planning there is no need to get caught out by the cold. I have also read on here I think that some people pump a bit of antifreeze and water into the system the night before, you then just pump and flush it through in the morning with pure water, not that I've tried it.
Simon